This invention relates to drying ink on a medium and, more particularly, to drying an image created by a liquid ink printer by passing air over the image while heating the image by conduction.
A key requirement of liquid ink printers, particularly color printers, is that the previous image must be dried before a subsequent image can be written thereon. Drying can be achieved by using radiant energy to dry the fluid. However, this method is not preferred because of the long distance required for providing a heater in the process direction (requiring a long machine with a large footprint), and the possibility of fire or explosion due to the evaporating carrier fluid, if the carrier fluid or medium is flammable. Further, the heated image-bearing medium may change its shape as the temperature thereof increases. This severely complicates, or makes impossible, the registration of the color separations.
Another drying method includes blowing room temperature air across the wet surface to vaporize the fluid. Due to the simplicity of this approach, this method is preferred in printers that operate at very low process speeds. However, very high flow rates or very high volumes of air will be required to dry images in high productivity applications, which makes this method impractical. Further, this method may result in an image that is not uniformly dried across the process direction, leaving wet areas at the edges of the image.
With reference to FIG. 1, a schematic illustration of a conventional single pass color printer, generally indicated at 10, is shown where a color image is created by superimposing color separations. The image processing involves passing the medium 12 over the writing head 14 to form a latent image for the first color 16. The medium 12 then passes over a development station 18 and a wet, visible image is created. The wet image is then moved past a drying station 20 which removes excess carrier fluid from the liquid image thereby preparing the image to receive the latent image for the next color 22. An example of this printer architecture is disclosed, for example, in U.S. Pat. No. 5,420,673. In such printers, room temperature air is blown across the wet image though a specifically designed channel to make more efficient use of the air. These dryers, although more effective than the dryers discussed above, are inadequate at high process speeds. The efficiency of these dryers is acceptable at high speeds only when the drying length is increased. Increasing the drying length results in a longer machine and larger footprint. Further, sealing the air against a wide web is difficult and, as a consequence, this type of dryer becomes less efficient as air leaks past the medium.
Accordingly, there is a need to provide a liquid ink drying device for uniformly drying an image in the cross-process direction, which occupies a minimum amount of space in the process direction, and dries the image without affecting the registration of the color separations.
An object of the present invention is to at least fulfill the needs referred to above. In accordance with the principles of the present invention, these and other objectives are attained by providing an apparatus for drying a liquid image carried on a surface of a medium moving though a predetermined path from an upstream location towards a downstream location. The apparatus includes a device for moving air, such as a fan or blower. A plenum has an intake for receiving the air and an outlet permitting the air to exit the plenum. A channel structure communicates with the outlet of the plenum and is disposed generally adjacent to a surface of the medium carrying the image. The channel structure includes an upstream channel portion and a downstream channel portion such that air exiting the outlet of the plenum is diverted to flow towards the upstream location in the upstream channel portion and towards the downstream location in the downstream channel portion. A heater is associated with the medium to heat at least a portion of the medium and thus the image.
In accordance with another aspect of the invention, a method of drying a liquid image on a surface of a medium moving though a predetermined path provides a source of air moving in a first direction. The source of air is directed to move past the image (1) in a second direction transverse to the first direction, and (2) in a third direction opposite the second direction, to dry the image as the image moves through the predetermined path.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following illustrative embodiments and appended claims with reference to the accompanying drawings, all of which form a part of this specification.